﻿using System.Collections;  
using System.Collections.Generic;  
using UnityEngine;  
using UnityEngine.UI;  
  
[AddComponentMenu("UI/Effects/Gradient")]  
public class Gradient : BaseMeshEffect  
{  
    [SerializeField] private Color32 topColor = Color.white;  
  
    [SerializeField] private Color32 bottomColor = Color.black;  
  
    public override void ModifyMesh(VertexHelper vh)  
    {  
        if (!IsActive()) {  
            return;  
        }  
  
        var vertexList = new List<UIVertex>();  
        vh.GetUIVertexStream(vertexList);  
        int count = vertexList.Count;  
          
        ApplyGradient(vertexList, 0, count);  
        vh.Clear();  
        vh.AddUIVertexTriangleStream(vertexList);  
    }  
  
    private void ApplyGradient(List<UIVertex> vertexList, int start, int end)  
    {  
        float bottomY = vertexList[0].position.y;  
        float topY = vertexList[0].position.y;  
        for (int i = start; i < end; ++i) {  
            float y = vertexList[i].position.y;  
            if (y > topY) {  
                topY = y;  
            } else if (y < bottomY) {  
                bottomY = y;  
            }  
        }  
  
        float uiElementHeight = topY - bottomY;  
        for (int i = start; i < end; ++i) {  
            UIVertex uiVertex = vertexList[i];  
            uiVertex.color = Color32.Lerp(bottomColor, topColor, (uiVertex.position.y - bottomY)/uiElementHeight);  
            vertexList[i] = uiVertex;  
        }  
    }  
}  